This document describes particulate filter weigh-room recommended practices to provide guidance in the procedures and processes associated with gravimetric filter weighing of engine or vehicle particulate matter (PM) emissions. This recommended practice provides proper procedures to build and maintain a particulate filter weigh room or enclosure to meet the requirements of EPA's 40 CFR Part 1065 and ISO 14065 for obtaining low measurement uncertainty. The content of this recommended practice addresses the following areas: a Particulate Filter Weigh Room b Microbalance Requirements c Filter Conditioning and Handling Requirements d Weighing Process e Equipment Calibration and Maintenance